Process of underground gasification of coal



2 SHEETS-SHEET 1 ATTORNEYS April 22, y1952 l.. L. NEWMAN ET Al.

PRocss `0F UNDERGROUND GAsIFIcATIoN QF COAL Filed June' 1o, 1949 .am m o 2% ,T 2% n an s m a \\\M\ m m ./o o /o m o /o T w M .//4 \\7/ T 1,7/ r N f m WC. L b w L m Y Iwo o n o o So 5o v Y OP@ u w w o o o o o o o T Nm v m I Om v 4N .su I1. .U w..

April 22, 1952 L.. l.. NEWMAN ETAL PROCESS OF UNDERGROUND GASIFICATION OF COAL Filed June 10, 1949 2 SHEETS-SHEET 2 vll,

V -INVENTORS W//burn G. Schroeder Louis L, Newman avm M ATTORNEYS Patented Apr. 22, .1952

PROCESS OF UNDERGROUND GASIFICATION OF COAL Louis L; Newman, Washington, D. C., and Wlburn C. Schroeder, Clinton, Md., assignors to the United States of America as represented by the Secretary of the Interior Application June 1o, i949, serial No. 98,343

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 5 Claims.

The invention herein described and claimed may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to improvements in vthe process of underground gasification of coal and other 'carbonaceous materials .in situ, such as coal, lignite, oil shale and similar materials.

,Since the gasification of coal is essentially the conversion of its solid carbonaceous components, by means of oxygen-containing gases, into gaseousproducts, a primary object of the invention is to provide a .method of controlling the gasication of coal, underground, and to make the conversion of a :seam of coal to gaseous products proceed in a continuous manner.

A further `object of the invention is the carrying out o f the gasication of the coal in place,V in

such a way, that each area of the seam is entirely` gasifled, with the production of useful gases.

The broad idea of converting coal underground to `useful gases is old as shown in the recent review of this subject by J. D. Clendenin, in Chemical Engineering Progress, vol. `513, No. 11, pp. 581-584 (1947) which mentions thirty-one literature references.

Howeverin spite of al1 these investigations.

.commercial vsuccess in underground-gasication.

of coal `and other carbonaceous minerals has not been attained to date. The quality of the gas has been poor, Vgasification of the coal has been incomplete and serious operating difficulties have been encountered in sustaining and directing the underground gasification.

We'have now found, that all of these Objec tions .can be overcome and a uniform grade of useful l-.;\gases obtained, when the underground operations are carried out .according to our in vention. 1 These and other obects are achieved by preparing the coal seam, beforehand, initiating gasication of the coal, then carrying out the operations so as to control both the rate at which the Aproduct-gas is generated, andcompletion of the 2 areas, with attendant destruction of the product-gases by combustion. This is an important feature of the invention and consists in the injection of non-combustible materials into the coal formation at strategic locations duing the course of the coal-gasification process.

Our improved method of initiating, sustaining and controlling the underground gasification of coaland other carbonaceous minerals is described in connection with the drawings, in which Figure 1 is .an underground plan view of lour process of carrying out the invention, and Figure 2 is .a v'ertical section, taken along the underground gal ery.

Referring to the drawing, A is a gallery, constructed in the coal seam, along the entire length of one boundary of the area to be gasied. A lre resistant wall W is built along one side of the gallery to prevent the combustion of coal, beyond this area. This wall is optional and may be disregarded, where operations are to be carried on, at both sides of the gallery. Vertical boreholes, A-l, A-Z, A-3, etc., which are 10-20 inches in diameter, are drilled from the surface of the ground down to gallery A. These boreholes are spaced about 300 feet apart, along the surfaceofthe ground and in an approximately `straight line. This distance between these holes may vary in different types of deposits. Additional rows of boreholes, are drilled down to the coal seam. These are designated as B-l, B-2, B-3, etc., C-I, C-2, C-3, etc., and D-I, D-2, D-3, etc., in Figure l. These rows are parallel to each other and to the outer row A-I A-2, A-3, etc., and are approximately 150 feet apart, with the holes in alternate rows, staggered, as shown in the drawing. This arrangement leads to a net-work of boreholes, in which the distance between holes in any row is about 300 feet andthe distance between contiguous holes in adjacent rows is about 200 feet. Specifically, the distance from A-I to A-2 is about 300 feet, `and the distance from A-I, or A-2 to B-l is about 200 feet. This results in forming between the contiguous holes in adjacent rows areas of similar triangular shape, as shown in the drawing. Each of the boreholes in rows A and B are connected directly to line AA handling air and line AG handling the produced gas. Similarly, each of the boreholes in rows C and D are connected to line CA .handling air and line CG handling gas, respectively. All the air lines are connected to manifold AM supplied by a blower BL, and all producer gas lines are connected to manifold GM, with an exhauster GE for removing the gas to a gas holder (not shown) The flow of air and gas is controlled by suitable valves, installed in the respective lines (not shown).

Besides the larger boreholes, for admission of air, or other oxygen-carrying gases, to the coal seam, and removal of the produced gases to the holder a third series of boreholes of much smaller size (3-4 inches) are drilled down to the coal seam, which is to be gasied. These are designated as A-Ia, A-2a, A-'a, etc. ,B-lb, B-Zb, B-3b, etc. in the drawings.

The role of these holes forms an important feature of our invention, and they play a major part in controlling and directing the course of the 'gasification operation, as will be described later on.

Having completed the necessary boreholes down to the coal formation, as indicated in the drawing, the actual operation of the process of coal gasification is carried out as follows:

Gallery A is lled with combustible material,

which may be pieces of broken coal taken from the same formation, pieces of coal from a richer formation, low-grade coal impregnated with oil, or in some cases combustible woody materials. This combustible material is ignited in any suitable way, for example by means of therrnite bombs, at several alternate locations such as at A|, A-3, A-5, etc. The number to be ignited will depend on the extent of the operation and the quantity of produced gas required. After the ignition of the combustible material at the designated locations, air or other oxygen-containing gases, are blown down these alternate boreholes to support the desired combustion. The regulating valves on each alternate pipe are manually adjusted to yield approximately equal amounts of air to each producing borehole.

The combustion of the coal or other carbonaceous mineral results in the formation of carbon dioxide, carbon monoxide and some distillation products, which together with,the nitrogen from the entering air are removed through the alternate boreholes A2, A-fl, A-, etc. and sent to the gas holder.

AS the combustible material in gallery A be` tween the boreholes is consumed by the oxygen of the entering gas, heat is generated and the roof subjected to this heat melts and sags, as was observed in Bureau of Mines'tests recently carried out at Gorgas, Alabama.

As the roof sags it partly lls the gallery and causes the entering gas to ow around the fallen roof, along the face of the coal seam, corresponding to the curved lines between adjacent holes, as shown on the drawing.

In the event that there are voids in the fallen roof, whereby the oxygen-containing gases may leak back to the adjacent' hole and burn the make gas instead of the solid carbonaceous material, non-combustible solidifying material, such as fluid cement, mixtures of mud and oil, rock dust and water, or a special mixture for sealing cracks known as gunite is injected into the formation through the smaller holes A-Ia., A-Za,

etc. In this way the combustion is maintained in the coal seam and a uniform production of useful make-gas is maintained.

Detection of leaks in the fallen roof is clearly shown by a drop in quality of the make gas which condition indicates that some of the make-gas is being consumed.

When most of the carbonaceous material between sets of boreholes, such as A-3, A-4 and B-3, as indicated on the drawing, has been gasied as shown by a falling-off in the quantity of make-gas the flow of gas from borehole A-4 is discontinued, and after suitable purging the ilow of air and gas is reversed to complete gasification of the combustible material in the indicated area. Then the burning area reaches borehole B-3.

Operations are now shifted to row B until the whole area of the second row is burned out as indicated by the curved lines on the drawing.

Emphasizing again the importance of the smaller boreholesA-Ia, B-Zb, C-3c, etc., they are provided for the purpose of introducing the inert, non-combustible material, between pairs of inlet and outlet holes, such as A-I and A2, to close any voids away from the burning face of the coal, thereby preventing the bypassing of the entering oxygen-containing gas, which might burn the make gas before it reaches the exit pipes. This is an absolutely essential step for good control of the gasiiication process. In certain special cases additional small holes, for the introduction of inert, non-combustible material may be drilled between the parallel rows of holes in order to improve control of the coal gasification.

While our disclosure shows one form of an operation, in which burning proceeds away from the retaining Wall, it is obvious to those skilled in the art that the operation can also be carried out on the other side of the gallery, in the absence of the re resistant wall either vsirmiltaneously or consecutively.

Having described our invention, We claim:

1. An improved process for rapidly gasifying large areas of underground-carbonaceous minerals with a minimum of underground work, involving the simultaneous use of a plurality of boreholes from the surface of the ground to the bed of the carbonaceous mineral, comprising the steps of forming a gallery of considerable length in a bed of carbonaceous mineral, forming a first set of boreholes communicating from the surface with said gallery, forming a plurality of additional sets of boreholes essentially parallel to, and spaced laterally from said rst set and from each other, and extending from the surface to said bed of carbonaceous mineral initiating combustion within said gallery, supplying oxygen-containing gas to said bed through alternate boreholes'of said rst set thereby maintaining a combustion zone along said gallery at the face of said carbonaceous mineral, removing the gases produced from intervening boreholes of said first set, continuing to supply oxygen-containing gas to, and to remove produced gas from, said rst set of boreholes thereby advancing the combustion zone toward said second set of boreholes along a line essentially parallel to said gallery, transferring the operations of supplying oxygencontaining gas and of removing-produced gases to said second set of boreholes as the combustion zone reaches said second set, and continuing to advance said combustion zone in like manner toward successive sets of boreholes, thereby rapidly and systematically advancing said combustion zone into said bed of carbonaceous mineral along a line essentially parallel. to said initial gallery.

2. A process in accordance with claim 1 in which the carbonaceous mineral comprises coal.

3. A process in accordance with claim 1 in REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Namem Date 876,626 Frasch Nov. 12, 1907 Ranney et al Aug. 9, 1932 FOREIGN PATENTS Number Country Date 523,333 France Apr. 19, 1921 OTHER REFERENCES Subterranean Gasicaticn of Coal, G. O. Nusinov, 1946, Canadian Chemistry and Process Industries, June 1945 (pages 29-32). 

1. AN IMPROVED PROCESS FOR RAPIDLY GASIFYING LARGE AREAS OF UNDERGROUND CARBONACEOUS MINERALS WITH A MINIMUM OF UNDERGROUND WORK, INVOLVING THE SIMULTANEOUS USE OF A PLURALITY OF BOREHOLES FROM THE SURFACE OF THE GROUND TO THE BED OF THE CARBONACEOUS MINERAL, COMPRISING THE STEPS OF FORMING A GALLERY OF CONSIDERABLE LENGTH IN A BED OF CARBONACEOUS MINERAL, FORMING A FIRST SET OF BOREHOLES COMMUNICATING FROM THE SURFACE WITH SAID GALLERY, FORMING A PLURALITY OF ADDITIONAL SETS OF BOREHOLES ESSENTIALLY PARALLEL TO, AND SPACED LATERALLY FROM SAID FIRST SET AND FROM EACH OTHER, AND EXTENDING FROM THE SURFACE TO SAID BED OF CARBONACEOUS MINERAL INITIATING COMBUSTION WITHIN SAID GALLERY, SUPPLYING OXYGEN-CONTAINING GAS TO SAID BED THROUGH ALTERNATE BOREHOLES OF SAID FIRST SET THEREBY MAINTAINING A COMBUSTION ZONE ALONG SAID GALLERY AT THE FACE OF SAID CARBONACEOUS MINERAL, REMOVING THE GASES PRODUCED FROM INTERVENING BOREHOLES OF SAID FIRST SET, CONTINUING TO SUPPLY OXYGEN-CONTAINING GAS TO, AND TO REMOVE PRODUCED GAS FROM, SAID FIRST SET OF BOREHOLES THEREBY ADVANCING THE COMBUSTION ZONE TOWARD SAID SECOND SET OF BOREHOLES ALONG A LINE ESSENTIALLY PARALLEL TO SAID GALLERY, TRANSFERRING THE OPERATIONS OF SUPPLYING OXYGENCONTAINING GAS AND OF REMOVING PRODUCED GASES TO SAID SECOND SET OF BOREHOLES AS THE COMBUSTION ZONE REACHES SAID SECOND SET, AND CONTINUING TO ADVANCE SAID COMBUSTION ZONE IN LIKE MANNER TOWARD SUCCESSIVE SETS OF BOREHOLES, THEREBY RAPIDLY AND SYSTEMATICALLY ADVANCING SAID COMBUSTION ZONE INTO SAID BED OF CARBONACEOUS MINERAL ALONG A LINE ESSENTIALLY PARALLEL TO SAID INITIAL GALLERY. 